1. Field of the Invention
This invention relates generally to a method for controlling and improving production or manufacturing processes using production data and calculation of specific variables to provide meaningful measurements for the production processes and, in particular, to a method for calculating cost of yield measurements for a multiplicity of production and manufacturing processes.
2. Description of Related Art
One goal of a manufacturing plant is to produce goods (or services) at a low enough cost to allow the company to make a sufficient profit selling them. One measurement frequently used to track the performance of the manufacturing plant is product yield. The yield is defined as the number of good parts or units shipped from the plant, divided by the number of parts or units started. Each product in a factory will routinely have a target yield which, if met, ensures that the company's cost targets are met. Traditionally, if the actual yield of a product falls below the target yield established for it, resources will be applied to correct whatever problem is lowering the yields. The resources (which are typically limited) may include, for example, manufacturing engineering analysis, equipment improvements, or new equipment, all of which, and others, that have monetary value.
In a large factory with many products running simultaneously, multiple products will be below their yield targets by varying amounts. However, applying limited resources to the products farthest behind their targets may not be the most efficient way to allocate them because other factors, such as, unit cost are not considered.
In a typical manufacturing plant having many products being processed or manufactured, the manufacturing process generally begins with a quantity of pieces to be processed. However, typically, after processing, a quantity of the pieces are not fit to be sold, or do not meet quality standards. This results in a loss of parts each time the process is run. Further, the process may or may not meet expected yields based on the number of pieces started and the number of post process pieces passing inspection or pieces which are shippable.
Thus, each product will have an expected number of parts to be shipped, which will be somewhat less than the number of parts started. The ratio of the number of parts shipped to the number of parts started is the actual yield. A plant will have an expected value for this yield (known as the “expected yield” or the “plan yield”). In a best case scenario, the actual yields are at or above their expected (or plan) values, and the plant is producing what is expected, and is profitable. However, in a typical manufacturing environment, expected yields are high and many products may not attain the expectations. The plant must apply it's limited resources (i.e., manpower, purchasing, research) to resolve whatever problems are preventing the products from achieving their expected yield.
A common difficulty related to the expected yield and the lack of meeting expected yields is that there are not enough resources to solve all the plant's problems simultaneously. A series of problems and decision may have to be resolved, such as, which problem to address first, how much time and money to expend on each problem for each process, and the extent of research investment.
Previous methods disclosed in the prior art prioritizes problems by addressing the product with the greatest difference between actual yield and expected yield. If all products are the same, then selecting the one that is the farthest off the plan could be a reasonable way to allocate scarce resources. However, products can vary in a multitude of ways, such as, for example, their cost of material, sale price, cost of manufacture, etc. Therefore, a plurality of factors need to be taken into account when prioritizing product manufacturing. For example, a single comparison, such as actual yield vs. expected yield, may show that a first product has a lower yield than a second product. However, the second product may cost much more to manufacture then the first product. Thus, it may actually be more cost efficient to spend resources on the second, higher yield, product.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for controlling manufacturing costs by calculating and comparing significant data to determine which manufacturing processes should receive resources for enhancement.
It is another object of the present invention to provide a method for ascertaining costs of manufacturing processes which is straightforward in application.
A further object of the invention is to provide a method for calculating measurements of performance of multiple processes.
It is yet another object of the present invention to provide a method which compares a plurality of measurements of performance of multiple processes.
It is yet another object of the present invention to provide a method for calculating measurements of value of production processes and provide meaningful data for allocating production resources.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.